1. Field of the Invention
The present invention relates to a transfer device for use with standardized mechanical interface (SMIF) systems for facilitating semiconductor wafer fabrication, and in particular to a transfer mechanism for gripping and transporting a reticle between a storage and transport container and a process tool.
2. Description of the Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
The SMIF system provides a clean environment for articles by using a small volume of particle-free gas which is controlled with respect to motion, gas flow direction and external contaminants. Further details of one proposed system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 xcexcm to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half micron (xcexcm) and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with 1 xcexcm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.2 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
A SMIF system has three main components: (1) sealed pods, having a minimal volume, used for storing and transporting workpieces and/or cassettes which hold the workpieces; (2) enclosures placed over access ports and workpiece processing areas of processing equipment so that the environments inside the pods and enclosures (after having clean air sources) become miniature clean spaces; and (3) a transfer mechanism to load/unload workpieces and/or workpiece cassettes from a sealed pod without contamination of the workpieces from external environments.
Workpieces such as reticles are transferred around within a reticle or semiconductor wafer fab within SMIF pods which are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which the reticles may be stored and transferred. In order to transfer reticles between a SMIF pod and a process tool within a fab, a pod is typically loaded either manually or automatedly on a load port on a front of the process tool. Once the pod is positioned on the load port, mechanisms within the port door unlatch the pod door from the pod shell so that the reticle may be transferred from within the pod into the process tool.
When transferring a reticle either automatedly or manually between a pod and the process tool, it is desirable to minimize contact with the upper and lower surfaces of the reticle. Any such contact may generate particles and/or affect the pattern etched in the reticle. In view of this minimal contact, the engagement between the reticle and gripping mechanism must be minimal and precisely controlled. It is therefore necessary to precisely position a gripping mechanism in the desired orientation to the reticle when gripping and transferring the reticle.
In order to transfer reticles in conventional systems, an input/output device is provided for receiving the reticle and separating the reticle pod. Thereafter, a three degrees of freedom (r, theta and z) workpiece handling robot is used to transfer the reticle from the door of the reticle pod onto the support plate within the minienvironment. Thereafter, a second workpiece transfer robot is used to transfer the reticle within the process tool. This arrangement takes up a significant amount of space in front of the process tool.
It is therefore an advantage of the present invention to provide a reticle transfer system for transferring reticles between a storage and transfer container and a process tool without exposure to contaminants and/or particulates surrounding the container and process tool.
It is another advantage of the present invention to provide a reticle transfer system which may be precisely and easily positioned to grip a reticle to be transferred.
It is a further advantage of the present invention to provide a reticle transfer system having a small footprint.
It is a still further advantage of the present invention that there is no contact with the container door inside of the seal zone (i.e., where the shell meets the door) to prevent particulate generation in that area.
These and other advantages are provided by the present invention which in preferred embodiments relates to a reticle transfer system. The transfer system includes a load port comprising a port door and a port plate circumjacent about the port door. Once a reticle-carrying container is loaded onto the load port, mechanisms within the port door decouple the container shell from the container door. Thereafter, the port plate with the container shell supported thereon is raised upward while the port door and container door remain stationary to separate the shell from the door so that the reticle within the container may be accessed.
The reticle transfer system according to the present invention further includes an arm assembly having a transfer arm capable of rotation and translation, and a gripping mechanism affixed to the end of the transfer arm. Once the shell has been separated from the door, the gripping mechanism is rotated and translated to a position adjacent the reticle so that it may access the reticle and transfer it from the container door and into the minienvironment through an access port in the minienvironment. From the minienvironment, the reticle may be transferred within the process tool by a workpiece handling robot. Once processing of the reticle is completed, the gripping mechanism may then transfer the reticle from within the minienvironment back to the container door.
In order to precisely, easily and repeatedly position the gripping mechanism in the desired location to grip and transfer the reticle, the gripping mechanism includes four downwardly extending posts spaced apart from each other so as to contact an outer rim of the container door as the gripping mechanism is lowered into position to grip and transfer the reticle. Once the four posts are seated in contact with the outer rim of the container door, the gripping mechanism is fixed in the proper position so that a pair of grippers within the gripping mechanism may rotate inward and grip the reticle. The posts also allow proper positioning of the gripping mechanism with respect to the container door and support platform within the minienvironment when returning the reticle to the container door or depositing the reticle on the minienvironment support platform.
The grippers of the gripping mechanism include a vertical surface for engaging the edges of the reticle. An elastomer such as an O-ring may be provided on the vertical surface to prevent slipping of the reticle upon engagement between the vertical surface and the reticle. Each of the grippers further includes an angled chamfer to engage a similarly angled section along the bottom edge of the reticle. The vertical surface, O-ring and chamfer of the gripper all allow the gripper to grip and transport a reticle without contacting the upper or lower surfaces of the reticle. The gripping mechanism further includes safety catches positioned under the reticle during transport. The safety catches do not contact the reticle during normal transport of the reticle, but are provided to prevent the reticle from separating from the gripping mechanism in the event the reticle gets dislodged from the chamfer on each of the grippers.